Re: Re: How to use IP/UDP/TCP checksum offload HW?

[Laurie Gellatly <laurie.gellatly@xxxxxxxxx>]

On 07/06/2011, at 10:57 AM, Grant Edwards <grant.b.edwards@xxxxxxxxx> wrote:

> On 2011-06-07, Laurie Gellatly <laurie.gellatly@xxxxxxxxx> wrote:
> 
>> I tried to enable this before without success.
> 
> Ah yes, I saw your (unanswered) post from a few years back asking
> about this.  I was hoping there had been some progress since then.
> 
>> I agree that its a waste of processor time when it can be performed
>> in hardware.
> 
> The last time I did some profiling, IP checksum calculation was a
> pretty significant bottleneck for TCP throughput.  Back in the NetBSD
> stack days, I got about a 20% improvement in throughput by writing my
> own assembly-language IP checksum routine for ARM7.  The FreeBSD C
> implementation and more recent versions of gcc do almost as well as
> hand-tuned assembly, but it's still a big percentage of CPU usage in
> TCP communications -- and it will be even worse now that I have a chip
> that does scatter-gather DMA.  A part for US $4 that has IP checksum
> offloading and scatter-gather DMA.  Back when I was a new grad...
> 
>> Must we look at the latest BSD code to see how to implement this?
> 
> Maybe.  Or there might be a simpler way to do it.  I would guess that
> the current FreeBSD has an API to configure this on a per-interface
> basis at run-time.
> 
> If we can assume that there is only one external interface, then we
> don't need any API or runtime checks, just a few strategic #if/#endif
> pairs and some CDL to control them.
> 
> -- 
> Grant
> 
> 
> -- 
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> 
So how do we progress this?
Should we offline exchange the mods we've each tried (code and CDL)?

...Laurie:{)

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